Potato French fries or fun fries are nice when hot and crispy but they will turn soggy real fast when left at room temperature.
Sometimes, my kids would bring back home the fries that they are unable to finish at fast food restaurants and it would a waste to throw them away.
The easiest way to heat them up amd make them crispy again is by frying them without oil using non-stick pan. There are loads of oil inside the fries and heating them up this way would cause all these excess oil to flow out onto the pan. A good way to get rid of the oil if you want to cut the calories! LOL!
Please use low heat to ensure that they are heated throughly and not burned.